Haha, I ask that question everytime Reeves is cast. But now I find it amusing actually, kind of like an inside joke in movies. The only movie I found him good in was I Love You to Death and his character was always high so...
It seems Branagh answered it himself in an interview from the time:
"[In the film he's a] truly malevolent, sexy, passionate, an obsessively evil creature. In leather trousers. Pretty tight - I'd pay money to see Keanu Reeves in leather trousers and I think a lot of other people would as well". The Age - 9th Sep 1993
I remember my friends and I paid to see it because of Keanu Reeves. We were not disappointed and I don't believe Kenneth was disappointed in Keanu's performance.
The only people routinely disappointed with Keanu's performances are those who have been told he can't act by the critics, and are scared to admit they enjoyed a performance lest they lose their credibility.
Obviously, many, many people enjoy KR's movies. If they didn't, they wouldn't make money and nobody would cast him. I don't have a problem with people not liking him but it bugs me that they think they know so much more about quality acting than the rest of us. Somebody is paying to watch Keanu's films...and it ain't just me :)
I loved him in this. In fact, I loved the whole cast. The film felt sexy, modern and fun.
I wouldn't call myself a Keanu Reeves fan (meaning I don't actively seek out his films to view), but I don't understand all the Keanu hate. I felt he was perfect as Don John.
I thought the others did a fantastic job, even though none of them could hold candles to Branagh and Thompson. It was like breathing for those two.